The invention relates to a varifocal optical system controlled electro-mechanically for focal distance variation and hence magnification, temperature correction focussing and finite distance focussing.
Such an optical system is known from British Pat. No. 2,141,260. The known system comprises a combination of four groups of lenses, i.e. two fixed groups one of which comprises a plurality of elements and two movable groups one of which also comprise a plurality of elements. The movements of the two movable groups are controlled by preprogrammed computing means to vary the magnification and to compensate for the perturbations due to temperature variations and proximity focussing. The computations performed by these means apply relatively complex interpolation algorithms if the computation data are introduced in the form of discrete digital values.
However, constant effors have to be made to give such systems a greater compactness and a greater simplicity so as to improve their reliability and reduce their cost. In connection with these efforts the known system has the drawback that it requires a considerable number of lens elements as well as a more complex computing means, which is contradictory to the requirement of simplicity and cost reduction.
It is an object of the invention to remedy this drawback and to provide means for reducing both the complexity and the cost of the known system.